1.Field of the Invention
The present invention relates to a liquid crystal display device which has a function of a contact sensor by disposing contact sensor electrodes so as to sandwich a liquid crystal layer formed between a first substrate and a second substrate between the contact sensor electrodes.
2.Description of the Related Art
In recent years, in liquid crystal display devices, there has been realized a liquid crystal display device having a sensor function called “a touch panel.” In this case, an instruction from a user is inputted to the touch panel by utilizing an icon or the like displayed on a screen of the liquid crystal display device.
The touch panel is installed on a display surface side of the liquid crystal display device so that instruction contents shown on the screen of the liquid crystal display device can be selected by either a hand of a human being or an object (for example, a stylus pen). When either the hand of the human being or the object directly touches the touch panel, the touch panel detects a position, within a panel surface, where either the hand of the human being or the object contacts the touch panel. The liquid crystal display device receives the contents instructed in accordance with the position where the contact is detected in the form of an input signal, and carries out an operation based on the input signal thus received.
A resistance film system (contact sensor system), an electrostatic capacitance system, or an optical system is known as a detection system of the touch panel.
It is studied that in the resistance film system (contact sensor system), the liquid crystal display panel and the touch panel are formed integrally with each other.
There is known a liquid crystal display device with a contact sensor in which for the purpose of forming the liquid crystal display panel and the touch panel integrally with each other in the resistance film system (contact sensor system), a pair of electrodes which contact each other when the user presses the panel surface with his/her finger or the like are formed on two sheets of substrates sandwiching the liquid crystal layer between them, respectively. Here, the pair of electrodes will be referred hereinafter to as either “first and second sensor electrodes” or “touch electrodes.” This liquid crystal display device with the contact sensor, for example, is described in Japanese Patent Laid-Open Nos. 2007-52369, 2007-95044,and 2001-75074 (referred to as Patent Documents 1, 2 and 3,respectively, hereinafter).
In the liquid crystal display device, the liquid crystal is enclosed between two sheets of substrates, thereby forming the display panel. In addition, in the liquid crystal display device, spacers for maintaining a distance (cell gap) at which the two sheets of substrates are opposite to each other are disposed between the two sheets of substrates in suitable size and with suitable density, thereby adjusting a strength which the display panel should have in a phase of pressing of the display surface side. When the entire disposition area of the spacers is large, the substrate on the display surface side is hardly bent by a pressing force, and also the first and second sensor electrodes do not readily contact each other. On the other hand, although the entire disposition area of the spacers is small, the first and second sensor electrodes readily contact each other, the strength of the display panel is insufficient.
Thus, the first and second sensor electrodes have to be made to readily contact with each other in a state in which the spacers are suitably disposed between the two sheets of substrates so as to obtain the desired panel strength. For this reason, in the liquid crystal display device described in Patent Documents 1, 2 and 3, “a height adjusting layer” having a height (a size in a thickness direction of the liquid crystal) smaller than that of each of the spacers is formed on at least one side of the first and second sensor electrodes. Thus, a gap defined between the first and second sensor electrodes (hereinafter referred to as “a sensor gap”) is determined depending on the cell gap, the height of the height adjusting layer, the electrode thickness, and the like.
Even the contact caused by application of a small external pressure can be detected as the sensor gap is smaller. Therefore, it is better that the sensor gap is small to a certain extent from a viewpoint of enhancement of the sensitivity.
On the other hand, when the sensor gap is too small, the sensitivity becomes too high. Thus, in the resistance film system, the optical sensor gap is set mainly based on a difference in height between each of the spacers, and the height adjusting layer.